I. Field of the Invention
The present invention relates generally to auxiliary axle systems for load-hauling vehicles and, more particularly, to a stowable tag axle system that includes a safety latch which positively latches the axle in the stowed position when the axle is retracted or disabled for repairs. The invention provides an improved latching system for securing the tag axle which has a compact and unitary construction which readily installs on a truck body, is easily positionally adjusted and in which the mechanism is shielded from clogging debris and corrosive materials in the case of a transit mixer application.
II. Related Art
Optionally deployable auxiliary axle systems are well known and often associated with a variety of types of load-hauling vehicles, particularly those accustomed to time-varying loading, such as dump trucks, refuse collection vehicles and transit concrete mixers. Such vehicles typically include a chassis or frame, a cab and a dedicated truck body mounted on the chassis behind the cab. Such vehicles also include a forward steering axle placed near the front of the cab and one or more sets of drive axles spaced behind the steering axle, the drive axles often being provided in a dual axle arrangement. The auxiliary axle systems furnish additional load carrying capacity by adding an axle for assisting the steering and drive axles in supporting the load and in adjusting the inter-axle distance or increasing the overall front-to-rear axle span distance for the vehicle. In this manner, not only does the tag axle system assist in balancing the load carried by, for example, a transit mixing cement truck, but generally it also enables the truck to carry a higher legal total payload than would otherwise be permitted because weight restrictions placed on vehicles traveling over highways are typically measured in terms of load per axle in combination with overall spacing between the vehicle axles.
Examples of such auxiliary axle assemblies that can be selectively engaged with the ground are shown, for example, in U.S. Pat. Nos. 5,897,123 and 5,018,755. Thus, it is known to have tag axle systems generally consisting of a rear tubular cross member carrying spaced wheel assemblies and carried by a pair of spaced tag axle arms which, in turn, are pivotally mounted to the rear portion of a truck chassis according to a generally known arrangement. Linear reciprocating operating devices, typically hydraulic cylinders, or pneumatic devices are employed to pivot the tag axle system between a raised or stowed position and a lowered or ground-engaging position.
To assure that the tag axle assembly will remain in the elevated or stowed position until it is intentionally lowered to the ground-engaging position, it is known to add some type of external latching mechanism such as that which is shown in FIG. 1 which illustrates a fragmentary side elevational view of a transit mixer with a tag axle assembly in its raised or stowed position. The view includes a portion of a vehicle frame 12, dual axle drive wheels 14, a mixing drum 16 partially supported by a rear mixing drum mount support frame 18 and a tag axle assembly which includes a pair of arms 20 pivotally mounted at one of their ends to the frame to the vehicle. A tag axle 22 carrying a tag wheel 24 is mounted to the opposite end of each arm 20. A common torque tube is shown at 26 and a shaped cam plate at 28 which cooperates with a cam follower wheel 30. Retraction air actuators are shown at 32 with associated arms 34. A further cam link assembly is provided which includes a pair of cam link arms, one of which is shown at 40 mounted from a pivot 42 and a pair of deployment air springs, one of which is shown at 44 which is affixed to the support frame 18 of the mixing drum using suitable means and to the cam link arms 40.
When the retraction actuators 32 are inflated, the arms 34 pull on the pivot members 36 connected to the torque tube cross member 26 to cause the tag wheels 24 to elevate to a retracted or stowed position. Conversely, deflation of the air actuators 32 and inflation of the deployment air springs 44 produces a downward force on the cam link arm 40 which is transferred to the arm roller 30 and then through the cam plate 28 of the tag assembly thereby lowering the tag axle wheels 24.
As previously indicated, to retain the tag axle assembly in the elevated position, there is further provided an external latching mechanism which includes a hook 50 pivotally mounted at one end to the mixing drum mount 18 and situated so that it can engage a pin 52 attached to the arm 20 of the tag axle assembly at an appropriate location. The hook is further provided with a biasing spring 53 and a pneumatic hook actuator at 54. Inflation of the actuator 54 overcomes the biasing of the spring 53 thereby releasing the pin 52 from the grasp of the hook 50. Otherwise, the biasing spring provides sufficient force to retain the pin 52 in the hook 50.
While this and other similar external hook arrangements have been known to function adequately, they consist of a number of parts which must be separately positioned relative to each other and aligned with the tag axle pin and the parts are exposed to mixing drum contents, acid washes and other hazards associated with the mixing and dispensing and cleanup of transit-mixed concrete. Accordingly, the parts readily become clogged with debris inhibiting operation of the spring and the pivoting of the hook to the point where operation of the hook 50 is impaired, thereby impairing the positive latching of the stowed tag axle system. In addition, corrosion of the separately attached parts leads to frequent difficult removal and replacement.
Accordingly, there remains a need for a compact and efficient safety latch system for tag axles which is easily removed and replaced as a unit and which does not have its integral operating parts exposed to the materials and cleaning agents associated with transit concrete mixing or other materials.
Accordingly, it is a primary object of the present invention to provide a compact modular safety latch for tag axles which is easily removed and replaced as an independent unit.
It is a further object of the present invention to provide a safety latch for tag axles associated with load hauling vehicles such as transit concrete mixers which has its moving parts shielded from contact with mixed cement, mixing materials and wash materials.
Other objects and advantages associated with the present invention will become apparent to those skilled in the art upon further familiarization with the specification, drawings and claims contained in this application.
The present invention provides a compact modular safety latch assembly for retaining an associated pivoting tag axle assembly in a stowed position when not in use and when the system must be retained in an elevated position with the vehicle shut off as for the performance of maintenance on the vehicle. The system employs a cylinder-operated, spring-biased pivoting hook arrangement assembled as a modular unit on a base plate for attachment to and behind the rear mixing drum mount support metal structure of a transit mixer or the like so that only the catch portion of the hook member protrudes through a slot in the support plate of the drum support structure. The modular safety latch system may be mounted through slotted openings in the plate of the vehicle which cooperate with slotted openings in the base or support plate directed in the opposite direction so that both vertical and horizontal adjustment is provided in the system for easy mounting and final alignment adjustment of the relative location of the latch hook so that the retention pin attached to the tag axle swing frame can be captured as desired. In this manner, the moving parts of the system are all located behind the metal support plate and are less likely to encounter clogging and corrosive materials in use.
The detailed embodiment of the modular safety latch itself includes a base plate carrying a pair of shaped, paced parallel flange members fixed to it and which, in urn, carry the latch hook pivotally journaled on a pivot pin spanning and mounted in the flanges. The latch hook is a member of dedicated shape having a top or forward curved hook section above the pivot and a lower or rearward tail section below the pivot and a fluid cylinder is provided which is bolted to the flanges in a manner such that extension of the rod associated with the cylinder overcomes spring biasing (below) pushes on the tail of the latch hook and pivots the latch hook away from and releases the latch pin (as the system is mounted on the vehicle). A counter-biasing tension spring extends between the latch hook and a member attached to the rear of the latch-operating cylinder to pivot and hold the latch against the cylinder rod and in a fully lowered or latched position when the operating rod is retracted or collapsed into the cylinder.
In operation, the operating cylinder is a normally retracted or collapsed and assumes this position when the fluid (hydraulic or pneumatic) pressure is lost in the cylinder. In this position, the biasing spring pivots the latch fully downward, placing it in the pin-capture position so that a stowed tag axle system will remain engaged by the latch hook until positive pressure operates the cylinder to extend the rod and overcome the spring tension thereby pivoting and raising the latch hook to release the pin.
In this manner, a relatively fool-proof latch system is provided in which the mechanism is substantially protected from the clogging and corrosion associated with past systems. In addition, the invention provides a modular unit which is readily installed, adjusted and replaced as necessary during the life of the vehicle.